1. Field of the Invention
The invention relates to a drilling tool with an exchangeable feed helix.
2. Discussion of the Prior Art
The applicant's German Utility Model GM 8,514,422 discloses a slip-on feed helix, which is secured axially by means of an axiall support. The drill shank has, in the region of the bottom edge of the slip-on helix, a recessed groove for receiving the supporting device, and radial expansion of the supporting device is prevented by non-positive or positive means.
Drilling tools with exchangeable feed helices are used predominantly for making perforations, with electric or pneumatically driven hammer drills being employed. The drill head is designed as a cross-type drill head or as a full drill head, fitted with carbide in either case. Tools of this type are illustrated, for example, in German Offenlegungsschrift Nos. 2,639,310, DE 3,044,775 A1 and DE 2,543,578 A1.
When perforations are made in fissured rock, the slip-on feed helix is exposed to high forces when, for example, rock becomes jammed between the drill-hole and the feed helix. Moreover, it can happen that, during drilling, the feed helix catches in the drill-hole. In the event of a further impact load exerted on the drill shank, the feed helix and the axial fastening, are pushed off from the shank or destroyed. Because the helix is limited and fixedly attached in the axial direction, axial play can arise as a result of the high axial vibrations, thereby suggesting that the particular design does not work very well.
The disadvantages described above apply both to continuous feed helices, that is to say feed helices with an outer structure similar to that of a drill, and to coiled feed helices.